1. Field of the Invention
The present invention relates to a position detecting system and to transmitting and receiving apparatuses for the position detecting system. More specifically, the present invention relates to a position detecting system for detecting a position of a moving body including a reflector reflecting a wave propagated through a space, and to transmitting and receiving apparatuses for the position detecting system.
2. Description of the Background Art
Conventionally, a position measuring apparatus for measuring a position of a moving body and a distance measuring apparatus for measuring a distance from a moving body have been known. In these apparatuses, light such as a laser beam is directed to the moving body, and the position of or distance to the moving body is measured using an incident angle of light reflected from a reflector provided on the moving body.
Japanese Patent Laying-Open No. 06-059016 discloses a position measuring device for a moving body that attains highly accurate measurement without requiring a preliminary measuring of the position of the reflector and registering the position in a circuit. In the position measuring device disclosed in this laid-open application, a light beam is emitted in rotary scanning manner from a moving body, light reflected from at least three optical reflectors arranged separately from the moving body is detected by the moving body, and based on the positions of respective optical reflectors and open-angle between each of the optical reflectors, the present position of the moving body is measured. The device includes: an optical detecting portion detecting an incident angle θ (1) of the light reflected from each of the reflectors on the moving body in a state that the moving body is placed on a first reference position and detecting an incident angle θ (2) of the light reflected from each of the reflectors on the moving body in a state that the moving body is placed on a second reference position away from the first reference position; and a calculating portion calculating the position of each of the reflectors based on an interval a between the first and second reference positions and on the incident angles θ (1) and θ (2) from each of the reflectors at both reference positions.
According to the invention disclosed in this laid-open application, for measuring the position of the moving body, first, at least three optical reflectors are installed at arbitrary positions on a plane on which the moving body moves. The moving body is placed on the first reference position, and in this state, the moving body emits a light beam in rotary scanning manner, and receives light reflected from each of the reflectors. As a result, the incident angle θ (1) of the reflected light on the moving body at the first reference position from each reflector is detected. Thereafter, the moving body is placed on the second reference position, and in this state, the moving body emits a light beam in rotary scanning manner and receives light reflected from each of the reflectors. As a result, the incident angle θ (2) of the reflected light on the moving body at the second reference position from each reflector is detected. Here, the interval a between the first and second reference positions can be set sufficiently smaller than the distance between each of the optical reflectors, and the interval can be measured with high accuracy by a well-known distance measuring means such as a rotary encoder provided on the moving body. Next, based on the measurements of incident angles θ (1) and θ (2), position of each optical reflector is calculated. At this time, the position of an arbitrary one of the optical reflectors is defined by the interval a between the two reference positions and two incident angles θ (1) and θ (2), and therefore, X-Y coordinates of the optical reflector can be calculated based on these data. Thereafter, position measurement of the moving body starts, in which light reflected from each of the reflectors is detected while rotary scanning of light beam takes place, and based on the position (X-Y coordinates) of each reflector and on the open-angle between each of the reflectors, the present position of the moving body is calculated. As a result, before measuring the position of moving body, the position of each reflector is measured with high accuracy by optical measurement, and the position of moving body is calculated based on the measurement data. Therefore, a highly accurate result of measurement can be obtained. Further, it is unnecessary to measure and register the position of optical reflectors.
Japanese Patent Laying-Open No. 06-317670 discloses an inter-vehicle distance measuring device having simple structure and capable of computing inter-vehicle distance in a short period of time, without requiring any human intervention such as visual estimation. The inter-vehicle distance measuring device described in this laid-open application includes an inter-vehicle distance calculating portion, which includes two sets of the following components: a laser beam transmitting portion transmitting a laser beam in a direction forward of the vehicle; a sweeping portion sweeping the laser beam; a laser beam receiving portion receiving the laser beam that has been transmitted from the laser beam transmitting portion and reflected by a reflector attached to the rear end of a vehicle in front; and an angle detecting portion detecting an angle at which the reflector exists, from the direction of arrival of the signal received by the laser beam receiving portion. The inter-vehicle distance calculating portion as such calculates the distance from the preceding vehicle from the angles detected by the two angle detecting portions respectively and an interval between the two laser beam transmitting portions stored in advance in a memory.
According to the invention disclosed in this laid-open application, a beam such as a laser beam is directed to a reflector at a rear end of a preceding vehicle, the direction where the reflector exists is detected, and based on this angle and the interval from the reflector, the inter-vehicle distance is measured. Therefore, different from the conventional measurement of inter-vehicle distance based on visual estimation, the inter-vehicle distance can be calculated with far higher accuracy. Further, two laser beam transmitting portions are provided on the vehicle, which are used independently to find the angle at which the reflector of a preceding vehicle exists. Therefore, even a distance from a preceding vehicle having only one reflector such as a motorcycle can accurately be calculated.
In the position measuring device described in Japanese Patent Laying-Open No. 06-059016, however, the light reflected from the reflector is detected on the moving body, and therefore, it is necessary to install the reflectors in advance. Accordingly, the position of the moving body can be measured only in a limited space, and the position of a moving body moving in an arbitrary place cannot be measured.
In the position measuring device described in Japanese Patent Laying-Open No. 06-317670, two laser beam receiving portions receive reflected light beams respectively, to detect the angle at which the reflector exists. This means that angle detection using reflected beam is performed twice. Typically, a light beam, including a laser beam, deflects as it proceeds through a space. Therefore, it follows that when the angle at which a reflector exists is to be detected by using the reflected light beam, there is an error resulting from the deflection. Accordingly, the position measuring device described in Japanese Patent Laying-Open No. 06-317670 involves twice the error resulting from the deflection, and hence, the measurement comes to have a considerable error.